LCD Screens‘How it works?’

LCD Screens Output devices

LCD ScreensLiquid crystal display (LCD) screens are visual display units.An LCD is made up of an array of pixels or picture elements.

An Array of pixels (liquid crystal display)

Each pixel contains red, blue and green

LCD Screens Output devices

LCD ScreensThere is a back light that shines through the pixel creating an image.

Back light shines through pixels (usually lit from bottom of the monitor)

Each pixel contains red, blue and green

An Array of pixels

LCD Screens Output devices

LCD ScreensDifferent combinations of red, blue and green are used to change the image.

Back light shines through pixels

Each pixel contains red, blue and green

An Array of pixels

LCD Screens Output devices

LCD ScreensThe pixels are positioned between two polarised grills.

Direction of light

Two polarisation filters or grills that are orientated 90 degrees to each other.

Filter A

Filter B

LCD Screens Output devices

LCD ScreensThe pixels are positioned between two polarised grills.

The polarised light must rotate through 90 degrees to pass through the other filter.

Filter B

Filter A

Light twisting through 90 degrees

LCD Screens Output devices

LCD ScreensHere are the pixels between the polarised grills.

Back light shines through pixels

The liquid crystals twist the light through 90 degrees

Two polarised grills

Light shines through

This allows the light to pass through filter B. Filter B

Filter A

LCD Screens Output devices

LCD ScreensAn electric current is applied to the crystals.

Back light shines through pixels

Two polarised grills

An electric current is applied to the crystals

Light shines through

LCD Screens Output devices

LCD ScreensWhen an electric current is applied separately to the red, blue and green crystals, the amount of twist in each one can vary the intensity of each and the final colour output.

Back light shines through pixels

An Array of pixels

Two polarised grills.

An electric current is applied to the crystals.

Light shines through.

The electricity passes through the crystals and changes how the crystals react, allowing some light and blocking other light.

LCD Screens Output devices

LCD ScreensThe electricity passed through the crystal, controls whether red, blue or green is output depending on the voltages applied to each crystal.

Back light shines through pixels

Two polarised grills

An electric current is applied to the crystals

Light shines through

LCD Screens Output devices

LCD ScreensThe diagram below shows an individual crystal, made up of red, blue and green light. In reality these are very small.

Electricity controls the colour twist and the amount of each light let through.

Red, blue and green crystals sandwiched between two polarised filters

Red Blue Green

LCD Screens Output devices

LCD ScreensHow it works:• Made up of an array of pixels with red, blue and green light

or picture elements.• A backing light shines through the array of pixels that show

different amounts of red, blue and green light. • The array of pixels are sandwiched between two polarised

grills.• When a current is applied to each crystal, the red, blue and

green light is twisted at different degrees, combining to make different colour pixels of light.

• The combination of mixing/blocking light forms the picture.

LCD Screens Output devices

LCD ScreensAdvantages:

• Smaller and lighter than equivalent CRT. • More energy efficient than CRT.

Disadvantages:

• Viewing angles can be smaller than from a CRT. • Dead pixels can be a problem with LCD Screens.